Gram Negative Bacteria Increase Non-Small Cell Lung Cancer Metastasis Via Toll-Like Receptor 4 Activation And Mitogen-Activated Protein Kinase Phosphorylation

Surgery is required for the curative treatment of lung cancer but is associated with high rates of postoperative pneumonias predominantly caused by gram negative bacteria. Recent evidence suggests that these severe infectious complications may decrease long term survival after hospital discharge via cancer recurrence, but the mechanism is unclear. Lung cancer cells have recently been demonstrated to express Toll-like receptors (TLR) that mediate pathogen recognition. We hypothesized that incubation of non-small cell lung cancer (NSCLC) cells with heat-inactivated Escherichia coli can augment cancer cell adhesion, migration and metastasis via TLR4 signaling. Incubation of murine and human NSCLC cells with E. coli increased in vitro cell adhesion to collagen I, collagen IV and fibronectin, and enhanced in vitro migration. Using hepatic intravital microscopy, we demonstrated that NSCLC cells have increased in vivo adhesion to hepatic sinusoids after coincubation with gram negative bacteria. These enhanced cell adhesion and migration phenotypes following incubation with E. coli were attenuated at three levels: inhibition of TLR4 (Eritoran), p38 MAPK (BIRB0796) and ERK1/2 phosphorylation (PD184352). Incubation of murine NSCLC cells in vitro with E. coli prior to intrasplenic injection significantly augmented formation of in vivo hepatic metastases 2 weeks later. This increase was abrogated by NSCLC TLR4 blockade using Eritoran. TLR4 represents a potential therapeutic target to help prevent severe postoperative infection driven cancer metastasis.What's new? Toll-like Receptor (TLR) signaling plays an important role in maintaining tissue homeostasis, a process that is deregulated in cancer. Here, the authors use heat-inactivated gram-negative bacteria as a new, clinically more relevant model to stimulate TLR signaling in cancer cells. Using this model, they augment lung cancer cell adhesion and migration in vitro and hepatic endothelium adhesion and metastasis in vivo, a phenotype dependent on TLR4 signaling and the activation of downstream effectors p38 and ERK1/2. These data underscore clinical data linking post-operative infection with cancer metastasis.